Halogen gas chemistries exhibit higher etch selectivity for germanium as compared to silicon and can therefore etch germanium faster than silicon. Similarly, halogen gases can etch silicon-germanium faster than silicon, and can etch germanium faster than silicon-germanium. Hence, halogen gas chemistries cannot (i) selectively etch a high-silicon content material from a high-germanium content material, and (ii) separate a germanium layer from silicon layer, a germanium layer from silicon-germanium layer, or a silicon-germanium layer from silicon layer. Such halogen gas chemistries can include fluorine and/or chlorine gasses.